UK moves towards ozone treatment
Ozone will soon become the biocide of choice for the UK industry, argues Mohamed Aly, UK water treatment specialist for ozone and UV system manufacturer WEDECO
Ozone oxidation systems offer enhanced operation, without residual chemical build-up in water systems, or the requirement for site storage, so it is no surprise that many industries worldwide are using them to control pathogens, biofouling and corrosion problems within their process and cooling water systems. But can they really out-perform chemical-based treatment?
Traditionally, industries such as power stations, food and beverage factories and many others have relied on chemical-based treatment to treat cooling and process water. Chemicals such as chlorine, however, fail to provide an efficient treatment solution for various reasons.
This can be due to the minimal or almost zero effect that they have on pathogens in biofilm; harmful by-products such as trihalomethanes; and also their tendency to saturate water systems with residual chlorides causing further corrosion problems to mechanical parts.
Another major issue surrounding the use of hypochlorite (chlorine) is storage.
With many industrial facilities having to store and protect tonnes of hypochlorite each day, responsibility and safety are key concerns. Stringent regulations for the documentation and protection of stored chemicals can be a time intensive task and the space required to safely contain this product is often a logistical inconvenience.
Despite the disadvantages associated with chlorine, it is widely considered to be the cheapest solution on the market which, until now, has been enough to cement its popularity in the UK. But this is starting to change.
Inadequately treated water can pose a major and potentially life-threatening risk. Within the warm and nutrient-rich conditions of an industrial cooling or process water system, naturally occurring pathogenic bacteria, such as legionella, e. coli and cryptosporidium, have the perfect environment to multiply considerably and become a serious hazard.
Additionally, there are major operational problems associated with these water systems when the microbiological activity is not controlled effectively. Two examples would be bio-fouling and corrosion, often resulting in high power consumption due to reduced heat transfer efficiency, costly shutdowns and the expensive repair and replacement of parts.
Pathogens and infectious microbes occur in natural water systems, soil and even air and it is therefore the responsibility of many businesses to safeguard against these pathogens.
Bio-fouling is the accumulation and attachment of micro-organisms to the inner surface of pipes, as well as the surface of heat exchangers and sensitive process units like reverse osmosis (RO) membranes and ion exchange resins. Bio-film usually forms on surfaces that are in direct contact with water, as a result of an extracellular polymeric substance (slime) that is produced by the pathogens in order to encase and protect them against biocides in the bulk water.
In favourable conditions the micro-organisms that are protected by the bio-film often promote localised microbial corrosion in process and cooling water systems. An additional contributor to the issue of corrosion is the elevated concentration of oxidising chemicals within the pipes as well as the vapours generated from the dosing system which cause surface deterioration within the key parts of the plant.
Legionella and other pathogenic bacteria are naturally present in environmental water sources such as lakes, rivers et cetera, and can easily colonise within industrial cooling and process water loops. If this is not prevented in any way, then there is a serious risk of causing an outbreak. According to the Health & Safety Executive, pathogenic bacteria outbreaks pose a serious threat to human health with Legionnaires’ disease being fatal in 12% of reported cases.
UK industry is beginning to follow in the footsteps of its continental counterparts in accepting ozone as a true contender for the treatment of water. So why are we seeing opinions change?
As with any technology; intensive development and scientific advances over time has generated solutions that are more powerful, more energy efficient, more reliable and easier to use. For industrial water treatment, ozone is the improved solution.
Systems like the Wedeco Ozone Complete System (OCS) series use ambient air to generate ozone on-site. It is then introduced to the water loop via side-stream injection and in some circumstances it can be introduced directly into the tanks or reservoirs by diffused aeration.
Once it has dissolved into the water, Ozone proceeds to oxidise organic contaminants and micro-organisms. Ozone is supplied as standard, ensuring ambient air monitoring instruments record zero levels at all times.
For added convenience, the dosing can be regulated automatically by a programmable logic controller (PLC). Controlling the usage of ozone in this way will optimise the efficiency of the treatment system and ensure the lowest possible operating costs.
The benefits of ozone are that it is:
- Environmentally friendly – Unlikehalogen-based biocides, once reacted, ozone molecules decay back into molecular oxygen, which allows cooling systems to operate efficiently at significantly high concentration factors. This improved method of operation can reduce the volumes of blow down water as well as the consumption rates of anti-scaling and anti-corrosion chemicals
- Increased disinfection efficiencies – With an oxidation potential of 2.07V, ozone is more than 50% stronger as an oxidiser and acts more than 3,000 times faster than conventional chlorine-based biocides. This additional power allows ozone to achieve disinfection by completely rupturing the pathogens’ cell membrane with no possibility for the micro-organism to develop any resistance against it
- Consents on discharge – Ozone treatment substantially reduces the level of absorbable organic halides (AOX) within the water system as well as decreasing the chemical oxygen demand (COD). This allows for trouble-free compliance with strict discharge regulations. (AOX < 0.15mg/l and COD <40mg/l can be easily achieved)
- No transportation or storage of hazardous chemicals – Ozone generators produce ozone on site. The generator, power supply unit, injection system and controls can be constructed on a skid or as a bespoke pre- tested and pre-commissioned containerised system that will occupy a relatively small footprint on any industrial site. The on-site production of ozone makes compliance with hazard procedures such as COSHH and COMAH as straight forward as possible
- Reduced cost – Wedeco ozone generators include a 10-year guarantee on production electrodes, with no consumable- parts over its lifetime. Routine maintenance is normally scheduled for pipe connections, valves and instrumentation servicing and calibration. As for the water system itself, less corrosion and biofouling will ensure maximum plant uptime, saving time and money on costly, unexpected breakdowns
The industry across America and continental Europe has been quick to spot the financial, environmental and performance benefits of ozone as a complete treatment solution for their water systems.
Now the UK is heading in the same direction. As the industrial market continues to strive towards the highest possible standards of working and best practice, Ozone will undoubtedly become the natural choice for cooling and process water treatment.
Ozone technology is proving to be the more efficient and reliable oxidation process that combines the three main benefits of less
human exposure to hazardous materials, lower operation costs and more importantly, no undesirable residual waste going back into the environment.
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